1. Field of the Invention
The present invention relates to a device for detecting and/or measuring a thermal phenomenon occurring in a product in a liquid state at a temperature in the range of temperatures swept by the detecting and/or measuring device.
The detecting and/or measuring device of the invention makes it possible to obtain the desired information regarding a product rapidly and accurately and permits easy automation of the acquisition of the detected values from the beginning of the thermal effect such, for example, as the temperature at which a phase change appears and/or more complete measurements.
The device of the invention is particularly well adapted to the determination of the beginning crystallization temperature of paraffins in diesel fuels.
2. Description of the Prior Art
Fuels for diesel engines have an increasing economic importance. The fuels can be roughly likened, from the point of view of their composition, to a solution of n-paraffins in a complex hydrocarbonated matrix. Because of the nature of diesel fuels, special problems are raised when the temperature of use is lowered and, for example, paraffin crystals appear, which causes difficulties, even making operation of the diesel engine impossible.
The fuels must then comply with requirements which, in France, are laid down by the Direction des Carburants which define Three relevant temperatures as follows:
PT: cloud point, or temperature at which the first paraffin crystals appear, PA0 TLF: limiting filtrability temperature, at which the paraffin crystals obstruct a mesh (45 .mu.m) of the fuel filter, and PA0 PE: flow point, i.e. the temperature at which a three dimensional paraffin network is created and the fuel can no longer flow.
American standards (A.S.T.M.) or European (E.N.) define the devices which permit determination of these three temperatures. As far as the cloud point is concerned, it is a question of the standard A.S.T.M. D-9766. The apparatus used is very unsophisticated, since it is by direct visual observation of a cooled product that the point is detected at which the first paraffin crystals appear. The accepted reproducibility is 4.degree. C.
An apparatus based on the principle of light diffusion have been constructed and is at the present time commercialized by, for example Normandie Labo, Malvern or Total.
Another method seems just as simple resides in detecting a release of heat by sweep calorimetry (A.C.D) when the first paraffin crystals are formed during cooling, i.e., when, in the n-constituent diagram, the liquidus is passed. It has been discovered that there was a linear relation between the measurement of the cloud point in accordance with the A.S.T.M. standard and the A.C.D. measurement. Similarly, the TLF and the PE may be found by A.C.D. with however non doped products. The reproducibility of the measurements is better than 0.1.degree. C., which is much better than the ASTM standard.
In some cases, the standard leads to erroneous results. In fact, in order to obtain the best yield from a noble product crude, refiners more often used heavy fraction cracking which leads to clear oils (L.C.O.) then mixed with the distilled fractions.
In these fuels, at the time of cooling, an unmixing can be observed (passing from one to two liquids) interpreted visually as being the cloud point. This error does not affect the A.C.D., which always observes the beginning of crystallization of the paraffins.